Look at Figure 29.28.

a. Calculate the relative molecular mass of leucine enkephalin (C₂₈H₃₇N₅O₇) using relative atomic masses. (A_r values C = 12.0, H = 1.0, N = 14.0, O = 16.0)

b. i. How is the peptide ionised before detection in the mass spectrometer?

ii. Why is this known as ‘soft ionisation’?

c. Why is there a peak at [MH + 1]?

d. An unexpected peak occurs at charge-to-mass ratio 578.1. This is caused by ionisation of the pentapeptide by a metal ion instead of an H⁺ ion. Which metal ion is responsible for this ionisation?

Transcribed Image Text:

100 MH+ 50 - 381.1 150 200 250 300 350 400 450 500 550 600 650 mle Abundance (%)